Ethyl Methyl Carbonate Research Articles

Facilitating Tetrafluoroborate Intercalation into Graphite Electrodes from Ethylmethyl Carbonate‐Based Solutions

AbstractKinetically facile intercalation of anions into graphite electrodes is essential for the good performance of dual‐ion batteries. The intercalation of BF4− anions into graphite electrodes is found to be strongly impeded in the electrolyte of 1.25 m LiBF4−ethylmethyl carbonate. For this, both the strong attraction between Li+ and BF4− clusters and the special solvation state of the anion are to blame. Two strategies are employed to tailor the solvation states of ions in the solutions, which prove easy and effective in facilitating anion intercalation into graphite electrodes.

Multiple transesterifications in a reactive dividing wall column integrated with a heat pump

This study addresses a reactive dividing wall column (RDWC) integrated with a vapor recompression heat pump (VRHP). The reaction applied to the system contains two consecutive transesterifications of dimethyl carbonate (DMC) and ethanol, which yields methanol (MeOH) as a by-product, ethyl methyl carbonate as an intermediate product and diethyl carbonate (DEC) as the final desired product. DEC is the only stable node of the five component reacting mixture. The location of the reaction region and feed stages affects the purity of the top product because the unstable node product is not pure MeOH but DMC-MeOH azeotrope. The VRHP pressurizes the top gas product stream and the compressed gas provides heat to the bottom stream of the ethanol recovery section. The optimization procedure minimizes the power consumption of the compressor with respect to the gas flow rate. The energy consumption in the RDWC integrated with a VRHP is reduced by 32.1% and the total utility cost is also cut by 21.6% compared with the conventional RDWC.

Opportunity for High Performance Lithium-Metal Batteries Enabled By in Situ Formation of Highly Stable Solid Electrolyte Interphase Layer

Lithium(Li)-metal has been considered most promising candidates as anode to increase the energy density of Li-ion batteries because of its ultrahigh specific capacity (3,860 mAh g-1) and lowest redox potential (-3.040 V vs SHE).1 However, unstable dendritic electrodeposition, low Coulombic efficiency and infinite volume changes severely hinder its practical uses.2 To stabilize the Li metal anode , the electrolyte used in this study, consisting of ethyl methyl carbonate (EMC) and fluoroethylene carbonate (FEC), ensures a stable robust solid electrolyte interphase (SEI) layer on the anode surface. In a LMBs using a commercialized Ni-rich Li[Ni0.6Co0.2Mn0.2]O2 (NCM622) and 1M LiPF6 in EMC : FEC = 3 : 1 electrolyte exhibit a high initial capacity of 1.8 mAh cm-2 with superior cycling stability and high Coulombic efficiency above 99.8 % for 500 cycles while delivering a unprecedented energy density. The present work also highlights a significant improvement in scaled-up pouch-type Li/NCM622 cells. Moreover, the postmortem characterization of the cycled cathodes, separators and Li-metal anodes collected from the pouch-type Li/NCM622 cells helped identifying the improvement or degradation mechanisms behind the observed electrochemical cycling.3 References A. Varzi, R. Raccichini, S. Passerini, B. Scrosati, J. Mater. Chem. A 2016, 4, 17251-17259.W.-J. Kwak, S.-J. Park, H.-G. Jung, Y.-K. Sun, Adv. Energy, Mater. 2018, 8, 1702258.S.-J. Park, J.-Y. Hwang, C. S. Yoon, H.-G. Jung, Y.-K. Sun, ACS Appl. Mater. Interfaces 2018, 10, 17985-17993.

Electrolyte Effects on the Intercalation of PF6 - into Graphite Positive Electrode for Dual-Ion Batteries

Different from traditional lithium-ion batteries (LIBs) which rely on Li+ as the only charge carriers, dual-ion batteries (DIBs) which use both cations and anions as electroactive species have received increasing attention due to their high power- density and low cost. So far, graphite has been shown to accommodate anions such as PF6 - and BF4 - with a capacity of close to 100 mAh g-1 and a potential of above 4.5V vs. Li/Li+ on the positive electrode [1-3]. Since the anions originate from the electrolyte, the electrochemical performances of the graphite electrode depend highly on the type of solvent used. Figure 1a shows the cyclic voltammograms of graphite (KS6, Timcal) electrodes in 3M LiPF6 dissolved in linear carbonate solvents of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC). We can see that by changing the solvent, the reaction peaks are completely changed. In particular, the lower onset potential at around 4.39 V vs. Li/Li+ suggests that it is easier for PF6 - anions to intercalate into graphite with EMC than DMC and DEC. Rate performances of graphite electrodes in the three different solvents are shown in Figure 1b. Interestingly, electrolyte with EMC solvent also gives much better rate capability than those with DMC and DEC. This is attributed to the difference in chemical interaction between the PF6 - anions and the solvent molecules. Further works on understanding how solvents’ properties, solvation structure and charge transfer impedances etc. affect the observed performances are underway and will be presented at the meeting.

Ethylene Carbonate-Free Electrolytes for High-Nickel Layered Oxide Cathodes

Layered lithium nickel oxide (LiNiO2), with a specific charge-storage capacity of almost 250 mA h g-1, an operating voltage of 3.8 V vs. Li+/Li, and a high packing density of above 3.4 g cm-3, offers a very high energy density approaching the limits of layered oxide cathode materials for lithium-ion batteries. However, despite early interests in the community, practical application of LiNiO2 was soon dismissed for a multitude of problems. This includes (i) poor thermal-abuse tolerance triggering battery thermal runaway at high states of charge, and (ii) severely restricted reversible capacity of < 200 mA h g-1 for desired cycle/calendar life owing to a high surface reactivity with conventional ethylene carbonate (EC)-based electrolytes and not fully reversible rhombohedral H2/H3 phase transition at > 4.2 V vs. Li+/Li. In spite of recent efforts on stabilizing ultrahigh-nickel layered oxides (Ni > 0.9) during battery operation through compositional tuning, the poor thermal stability and cyclability over a broad Li content range remain challenges of LiNiO2-based cathodes. Here we design nonaqueous electrolytes with exclusively aprotic acyclic carbonate solvents (such as ethyl methyl carbonate, EMC) tailored to an ultrahigh-nickel layered oxide cathode (LiNi0.94Co0.06O2). Common lithium-conducting salts (e.g., lithium hexafluorophosphate, LiPF6) and interphase-forming additives (e.g., vinylene carbonate, VC) are adopted in two model electrolyte systems. Assembled graphite|LiNi0.94Co0.06O2 pouch-type full cells in the two EC-free electrolyte systems show excellent long-term cycling performance of ~ 80% capacity retention after 1,000 charge-discharge cycles at 25 oC (1C, 2.5 – 4.2 V), notably superior to the same cells in the baseline EC-containing electrolyte (1.0 M LiPF6/EC-EMC(3:7)+2%VC). Through time-of-flight secondary-ion mass spectrometry coupled with lithium isotopic labelling and in situ X-ray diffraction, we demonstrate suppressed unwanted electrode-electrolyte reactions and irreversible structural degradation of LiNi0.94Co0.06O2 at highly delithiated states in the EC-free electrolytes during battery operation. In addition, through differential scanning calorimetry, we also show significantly inhibited self-heating of the ultrahigh-Ni layered oxide cathode at full charge in the EC-free electrolytes, outperforming charged LiNi0.8Co0.15Al0.05O2 in the EC-containing electrolyte. In summary, we present a facile approach of nonaqueous EC-free electrolytes to address the long-standing challenges of LiNiO2-based cathode materials for safer and long-life high-energy-density lithium-ion batteries.

Molecular Dynamics Simulations of Lithium Ion Battery Anode Interface in Battery Charging Process

The use of lithium-ion (Li-ion) batteries to power hybrid, plug-in hybrid, and electrical vehicles in recent years calls for greater battery charge rate than their applications in electric devices. These properties are largely caused by the phenomenon in the interface of electrode and electrolyte. For the battery charge rate, the process of Li+ desolvation in the interface and intercalation to graphitic anode are key factors. However, there are various hypotheses about Li+ desolvation and it has still not been clarified. Detailed understanding of the interface can accelerate the development of Li-ion battery. In this work, to gain an understanding of the Li+ desolvation in battery charging process, atomistic molecular dynamics simulations of the electrode/electrolyte interface at a constant voltage were performed. We utilize a modified version LAMMPS code implemented the novel computational approach to carry out the simulation of the electrolyte in the presence of electrodes and applied voltage. The approach for treating the model of battery interface held at a constant potential, which has necessity to calculate the nonperiodic cell in the surface normal direction, is based on effective screening medium (ESM) method [Otani and Sugino, Phys. Rev. B 73, 115407 (2006)]. The Poisson equation is solved with the help of the green’s function technic. The electrostatic potential V(z) was solved as following equation, V(z) = -∑q i|z i-z|/2ε 0 S 0, where ε 0 is the permittivity of vacuum, S 0 is electrode’s surface area, and q i is the charge of ith atom. If a potential difference V is applied across the two electrodes, then the charges are induced on each electrode surface to be V(z le) - V(z re) = V, where z le is the z of left side electrode surface and z re is right one. Prepared simulation model is the box with two edge plane of graphitic electrodes separated by an electrolyte which consists of 1M LiPF6 / ethylene carbonate (EC) / ethyl methyl carbonate (EMC) 30:70. The interelectrode spacing is 8 nm. We confirmed it is enough to describe the Electric double layer (EDL) of each electrodes with utilizing ESM-RISM method [Nishihara and Otani, Phys. Rev. B 96, 115429 (2017)]. To get the interface structure in EDL in short timescale simulation, preliminary runs for 3 ns at 298 K was carried out in the constant NVT ensemble with applied voltage of constant 20 V. After that equilibration runs for 3.8 ns at 298 K were carried out with applied voltage of constant 1 V. Finally production runs which modeling the charging process from 1 V to 4 V was carried. We discuss about the Li+ desolvation in battery charging process with observing electrolyte dynamics in EDL. Figure 1

Comsol Simulation of Hierarchical Ordered Porous Microstructure Electrode

High specific energy is always desirable in battery systems, especially for electric vehicles. A key towards improving specific energy for a particular combination of anode and cathode active material is to maximize the mass fraction of active material, which means minimizing the fraction of inactive material such as the separator, the binder, electrode additives for improving electronic conductivity, and the current collector. A seemingly simple strategy for maximizing the mass fraction of active materials is to make the electrodes as thick as possible. However, ion transport in thick electrodes can be particularly problematic since salt diffusion into and through the electrode pore space is slow and can easily limit the battery charge / discharge rate. An ideal microstructure is one that allows for direct line of sight or path for the electrode active material access to the electrolyte, for rapid ion-transport throughout the entire electrode thickness. Therefore, a need exists for electrode fabrication methods that create microstructures that maximize electrolyte transport, as is needed to achieve high-rate charging/discharging in electrodes having high mass loading. Optimal microstructures in electrodes help to achieve the ideal balance of active material and electrolyte mass to give high gravimetric and volumetric energy density. As to design a microstructure with the goal of Li ion salt transport facilitation, we synthesized ordered porous microstructure electrodes using combination of freeze cast and tape cast techniques. This method enjoys the combination of conventional tape casting, a main technique in manufacturing Li ion electrodes in industrial scale, and freeze casting. This study simulate two dimensional ordered porous electrode cross-sections and presents the electrochemical performance results of Mo-doped LTO in a electrochemical cell consist of a lithium metal anode, polymer separator, and liquid ethylene carbonate and ethyl methyl carbonate electrolyte. The electrochemical performance of ordered porous microstructure is investigated by varying electronic conductivity, tortuosity, particle size, electrode thickness, and C rate. We show that these engineered porous electrodes considerably reduces the electrolytes mass transport limitation and electrochemical response of electrode is independent of tortuosity, making it possible to synthesize ultra thick electrode for high energy and power density applications. Simulation results show that 10 micron thickness of wall and pore freeze tape cast Mo-doped LTO with electronic conductivity of 1 S/m, tortuosity as high as 10, electrode thickness of 458 micron and mass loading of 30 mg/cm^2 can deliver full capacity even at 2 C-rate.

Ionic polymer metal composites for use as an organic electrolyte supercapacitor

Choosing the right electrolyte for enhancement in energy storage and dissipation efficiencies of an electrochemical supercapacitor is a critical decision and a successful material choice could solve many issues faced by renewable energies such as wind and solar energy. Traditional aqueous electrolytes have been and continue to be used for their excellent electrolytic performance, but over past few decades, use of solid polymer electrolytes (SPEs) improved the performance of such devices by enhancing the power density and energy density. Platinum (Pt) incorporated ionic polymer metal composites (Pt-IPMCs) are being investigated for their applicability as solid polymer electrolyte (SPE) membrane for high-power supercapacitors as they have demonstrated improved performances in devices such as fuel cells, soft actuators etc. Pt nanoparticles were dispersed into a cubical Nafion membrane in a dense cluster (size distribution showing narrow). The Pt-IPMCs were tested using lithium hexafluorophosphate (LiPF6) in ethylene carbonate ((CH2O)2CO) and ethyl-methyl carbonate (C4H8O3) mixed in 2/1 volumetric ratio. Pt-IPMC resulted a lower internal voltage drop (0.15 V), higher ionic conductivity (0.46 mS cm−1), and higher specific capacitance (50.9 F g−1) compared with the commercial liquid electrolytes or Nafion 117. The average power density and energy density have improved by 19 and 17%, respectively by using Pt-IPMC electrolyte which could be ascribed to the decrease in the cell resistance or the increase of ionic conductivity. It should be noted that IPMC can be adopted as supercapacitor as well as soft actuator.

Synthesis of ethyl methyl carbonate via transesterification over molecular sieves and ZIF-8

An efficient catalyst system of molecular sieves and ZIF-8 was developed for preparing ethyl methyl carbonate from dimethyl carbonate and diethyl carbonate under mild conditions. We used a number of tools to characterize ZIF-8, including X-ray diffraction instrument and physical adsorption instrument and thermogravimetric analyzer. Chemisorption instrument was used to characterize its acid-base properties. We studied different factors associated with the yield. The catalyst leaching test showed that the reaction took place heterogeneously.The results indicated that the catalyst system of molecular sieves and ZIF-8 displayed excellent activity, selectivity and reusability. Furthermore, the addition of molecular sieves to ZIF-8 resulted in dramatic increases from 50.3% to 84.7% in the yield.

Synergetic Effect of Ethyl Methyl Carbonate and Trimethyl Phosphate on BF4- Intercalation into a Graphite Electrode.

LiBF4-ethyl methyl carbonate (EMC)-based solutions have not been successfully employed in dual-ion batteries (DIBs) mainly on account of few solvated BF4- intercalations into graphite positive electrodes. In this article, trimethyl phosphate (TMP) is introduced into 1 M LiBF4-EMC solution as the electrolyte solution for DIBs, thus revealing a synergetic effect in which the discharge capacity for the anion storage using 1 M LiBF4-EMC/TMP (8:2 by vol) (ca. 26.7 mA h g-1) is far superior to that for the batteries using 1 M LiBF4-EMC (ca. 2.7 mA h g-1) or 1 M LiBF4-TMP (ca.1.1 mA h g-1). In this case, the effects of TMP on LiBF4 in 1 M LiBF4-EMC/TMP electrolyte solutions are explored by conventional electrochemical tests, ex situ X-ray diffraction, in situ Raman spectroscopy, and nuclear magnetic resonance.

On the first coordination shell of lithium ion in linear carbonate solvents as electrolyte model for lithium-ion batteries: a computational study

The question of the number of carbonate molecules in the first coordination shell of the lithium cation is outstanding. This query has been already answered for cyclic carbonates like ethylene carbonate (EC), demonstrating a coordination number of 4. In this work, we attempt to solve such a problem for three linear carbonates including dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). For this purpose, we have calculated various Li+–carbonate clusters with the coordination number from 1 to 4 by using density functional theory at the B3LYP/6-31+G (d, p) level. A discussion has been made on favoring of Li+···O=C interaction over Li+···OC2 interaction in the coordination process of carbonates to the lithium cation. The IR spectra of the optimized clusters have been also computed to improve understanding of the Li+ interaction with the carbonyl group of the solvent. Thermodynamic functions of the coordination process such as Gibbs free energy (ΔG), heat of formation (ΔH), and entropy (ΔS) as well as binding energy (Ebin) have been obtained to explain the effect of alkyl chain of carbonates on the coordination. Our calculations show that the number of linear carbonate solvents coordinated directly to the lithium cation can be up to 3. Furthermore, it is observed that the interaction strength of the studied three solvents with Li+ is in the sequence DEC > EMC > DMC. This indicates that the dissociation constant of a lithium salt as an effective parameter for lithium-ion batteries could be higher in diethyl carbonate.

Zn-Co@N-Doped Carbon Derived from ZIFs for High-Efficiency Synthesis of Ethyl Methyl Carbonate: The Formation of ZnO and the Interaction between Co and Zn

In this work, a series of Zn-Co@N-doped carbon materials were prepared by pyrolysis of Co/Zn-ZIF precursors under a N2 atmosphere and used for high-efficiency synthesis of ethyl methyl carbonate (EMC) from dimethyl carbonate (DMC) and diethyl carbonate (DEC). The Co to Zn molar ratio and calcination temperature were varied to study the physical and chemical properties of Zn-Co@N-doped carbon materials identified by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), inductively coupled plasma (ICP), thermogravimetric analysis (TG) and temperature programmed desorption (TPD) analysis. It was deduced that the formation of a ZnO crystalline structure and the interaction between zinc and cobalt providing weak basic sites and strong basic sites, respectively, in different samples significantly affected their catalytic performance. The catalyst activated the reaction most effectively when the Co to Zn molar ratio was 1.0 and calcination temperature was 600 °C. With the DMC to DEC molar ratio controlled at 1:1, a superior yield of around 51.50% of product EMC can be gained over catalyst ZnCo/NC-600 at 100 °C with 1 wt% catalyst loading in 7 h.

Thermal degradation analyses of carbonate solvents used in Li-ion batteries

The thermal degradation of the electrolyte solvents of a Li-ion battery in an inert atmosphere was carried out using an assembly that allowed the quantification of the degradation products. The study of the vapour pressures and DSC showed that, in an inert and confined medium, the linear solvents, dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), become degraded at lower temperatures than those of cyclic solvents: ethylene carbonate (EC) and propylene carbonate (PC). Therefore, they were the ones that were studied under the following operating conditions: initial temperatures of 180 °C, 240 °C and 300 °C for three periods of 30 min, 60 min and 2 h. The thermal decomposition of DMC and EMC was observed under all of the conditions studied. This decomposition is maximum at a temperature of 300 °C and for a pyrolysis duration of 2 h. The species resulting from the pyrolysis of the DMC and EMC in the gas phase correspond to those identified during the global overcharge tests on a study cell containing these two solvents (excluding fluorinated species). The greatest similarity was observed for degradations carried out at 300 °C, whatever the duration. Thus, this study shows the important role of the thermal degradation of volatile solvents.

1,2,6-Oxadithiane 2,2,6,6-tetraoxide as an Advanced Electrolyte Additive for Li[Ni0.5Mn0.3Co0.2]O2/Graphite Pouch Cells

1,2,6-oxadithiane 2,2,6,6-tetraoxide (ODTO) as a novel electrolyte additive was evaluated in both uncoated and coated single crystal Li[Ni0.5Mn0.3Co0.2]O2/graphite pouch cells with 1.2M LiPF6 in ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7 by weight) as the electrolyte. ODTO passivates the graphite negative electrode at ∼1.4V (vs. Li/Li+) and also forms a solid electrolyte interphase layer at the positive electrode side. X-ray photoelectron spectra of cells filled with 1% ODTO demonstrate that ODTO mainly converted to sulfur-containing species at both electrode surfaces after formation. The performances of cells containing up to 5% ODTO and binary additive blends including 2% vinylene carbonate (VC) + 1% ODTO, 2% fluoroethylene carbonate (FEC) + 1% ODTO and 1% LiPO2F2 + 1% ODTO were evaluated and compared to cells with 2% VC, 2% FEC and 1% LiPO2F2. Ultra-high precision coulometry (UHPC) and long-term cycling show that 3% ODTO alone increased coulombic efficiency (CE) and led to high capacity retention for both uncoated and coated cells. Cells with uncoated NMC532 and additive blends containing 1%ODTO along with 1%LiPO2F2, 2% VC or 2%FEC showed virtually identical cycling performance to cells with coated NMC532 and the same electrolytes, suggesting that coatings are not required if effective additives are used.

How Ethyl Methyl Carbonate Assists Ethylene Carbonate in Co-Intercalating into Graphite Electrode with PF6−

Solvent dramatically affects the behavior of anion intercalation into graphite electrode in dual-ion batteries (DIBs). Our previous studies have confirmed that the intercalation of ethylene carbonate (EC) solvated PF6− is considerably suppressed. However, in this letter, we show that EC can apparently co-intercalate with PF6− into graphite electrode once ethyl methyl carbonate (EMC) is involved inside. In situ X-ray diffraction (in situ XRD), ex situ XRD, fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS) have been carried out to clarify the underlying reason.

Enhanced Electrochemical Performance of LiNi0.8Co0.1Mn0.1O2 Cathode with an Ionic Liquid-Based Electrolyte

An ionic liquid-based electrolyte consisted of N-methyl-N-propylpyrrolidine bis(trifluoromethanesulfonyl)imide (Pyr13TFSI), sulfolane (SL) and ethyl methyl carbonate (EMC) as co-solvent, lithium difluoro(oxalate)borate (LiDFOB) as Li salt for cathode material LiNi0.8Co0.1Mn0.1O2 (NCM811) is investigated in this study. The electrolyte with ionic liquid (IL) has improved safety characteristics and a wide electrochemical window that can reach 4.8V (vs. Li/Li+). The Li/NCM811 half-cells with the electrolyte display outstanding electrochemical performance, achieving a discharge capacity and capacity retention of 166.1 mAh g−1 and 97.6% after 100 cycles between 3.0 and 4.3V at 25°C. This excellent electrochemical performance is due to a thin and compact cathode electrolyte interphase (CEI) film formed on the surface of the LiNi0.8Co0.1Mn0.1O2 electrode derived from the electrolyte with IL and reduction of lithium dendrite formation. The film inhibits the volume change of the material during the charge-discharge cycles and maintains the structural integrity of the cathode material, which enhances electrochemical performance of the Li/NCM811 half-cells.

Communication—Microscopic View of the Ethylene Carbonate Based Lithium-Ion Battery Electrolyte by X-ray Scattering

Small angle X-ray scattering studies are conducted to gain insight of the microscopic structures on LiPF6/carbonates battery electrolyte. The result shows that ethylene carbonate (EC), with a cyclic structure, forms nanoclusters of ∼ 1 nm in linear carbonates ethyl methyl carbonate (EMC), diethyl carbonate (DEC), while it fully dissolves in a cyclic carbonate, propylene carbonate (PC). The ion pair of LiPF6 in carbonates is measured to be ∼ 6 Å in dimension, corresponding to the form of contact ion pair. The new microscopic structure the battery electrolyte reported herein is important for the understanding of non-ideal behavior of LiPF6 carbonate based electrolyte and thus the design of new electrolyte.

Liquid–Liquid Equilibria for Ternary Systems of (Ethyl Methyl Carbonate + Methanol or Ethanol + Water) at 293.15, 303.15, and 308.15 K

Liquid-phase composition values for {water + methanol + ethyl methyl carbonate (EMC)} and (water + ethanol + EMC) were determined at temperatures of 293.15, 303.15, and 308.15 K at 101 kPa. Thermod...

Electroanalytical evaluation of temperature dependent electrolyte functions for lithium ion batteries: Investigation of selected mixed carbonate solvents using a lithium titanate electrode

Abstract Characterization of materials for advanced lithium ion batteries (LIBs) represents an essential area of the contemporary energy storage technologies. The present work illustrates an electroanalytical framework for quantitative testing of liquid electrolytes for LIBs. The measurements explore a temperature range from 40 °C to sub-zero regimes, with a special focus on the electrolyte functions for low temperature applications. The test electrolytes include different combinations of ethylene, dimethyl, diethyl and ethyl methyl carbonate (EC, DMC, DEC and EMC, respectively) solvents, with LiClO4, Li bis(trifluoromethane)sulfonimide (LiTFSI) and LIBF4 salts. The experiments utilize the diagnostic features of electrochemical impedance spectroscopy (EIS), in combination with cyclic voltammetry (CV) and galvanostatic cycling. Temperature controlled measurements of two- and three-electrode EIS, coupled with CV, demonstrate how the electrolyte conductivity and electrochemical stability can be evaluated in a comprehensive approach. The compositions of the test electrolytes are optimized according to their temperature dependent ionic conductivities and their electrochemical windows. Two optimal electrolytes based on EC:EMC and EC:DMC:EMC mixtures are further examined for battery operations by galvanostatic cycling in a half-cell containing a Li4Ti5O12 anode. Consistent with the findings of the conductivity and electrochemical window measurements, the EC:EMC system exhibits superior performance in these half-cell experiments.

Possible carbon-carbon bond formation during decomposition? Characterization and identification of new decomposition products in lithium ion battery electrolytes by means of SPME-GC-MS

Commercially available lithium ion batteries (LIBs) of the 18650 cell format were aged with different cycling protocols. After cell opening and electrolyte extraction, the obtained electrolyte was characterized with respect to the occurring organic aging products. Therefore, gas chromatography - mass spectrometry (GC-MS) with standard liquid injection as well as solid phase microextraction (SPME) was applied. The composition of the pristine electrolyte and the main decomposition products have already been discussed in a preceding study. However, the SPME method provides access to study aging products, which are present in lower concentrations. Structural elucidation was done for several signals of interest. For ongoing validation of previously unknown compounds, selected standards were synthesized in order to compare fragment patterns and retention times. Three carbonates with butoxy-moieties were identified, although the longest carbon chain in the constituents of this specific electrolyte are the C2 chains of ethyl methyl carbonate (EMC) and ethylene carbonate (EC). Furthermore, the longest chain in standard carbonate based electrolytes in general is the C3-chain of propylene carbonate (PC). Thus, the formation of a carbon-carbon bond during cycling of LIB electrolytes has to be considered. In addition to the well-known transesterification reactions the occurrence of this type of reaction leads to a variety of new carbonate based decomposition products. Hence, their presence has to be taken into account with respect to possible influences on the interphases formed at the electrode/electrolyte interfaces.